In order to insert or take out loose-leaf paper sheets conveniently, a single-detent binder (also known as a loose-leaf ring binder) is widely used for a file folder or a note book. A typical single-detent binder mainly comprises an elongate curved housing, a pair of elongate baseplates, a plurality of ring shaped components and one or more control handles. The two longitudinal sides of the housing are bent inwards to form two inner sides. The pair of baseplates is located inside the cavity formed by the curved housing, so that one of the two longitudinal sides of each baseplate abuts upon the inner side of the housing while the longitudinal sides on the other side of the baseplates are interconnected in parallel, thus forming a central hinge possessing a pivot axis. Each baseplate is fixedly connected to a plurality of half ring shaped elements. At least one end of the loose-leaf binder is usually connected to a control handle, and the control handle is able to operate one pair of baseplates and move the central hinge upwards or downwards, so that the half ring shaped elements connected to the baseplates reciprocate between the open and closed positions.
A typical loose-leaf ring binder has a defect that the when the half ring shaped elements close, they cannot occlude together reliably. If the mechanism falls accidentally, the ring shaped components may be opened unexpectedly. A single-detent binder can also comprise a locking system, thus enhancing the locking function and preventing the ring shaped components from being opened unexpectedly. The locking system usually comprises a pull rod and a plurality of locking components. It would be desirable to reduce the time it takes to assemble the single-detent binder.